1. Field of the Invention
The present invention relates to diene compounds, in particular, co-dimer diene compounds. These compounds are prepared through the reactions of conjugated diene compounds with vinyl esters in the presence of a ruthenium salt. The invention especially relates to a chain co-dimer diene compound which is a promising raw material for preparing terpenes. Chain co-dimer diene compounds are obtained by reacting a 2-substituted-1,3-butadiene (a conjugated diene part) with a compound having a double bond at its terminal (a vinyl ester part). The invention also relates to a method of producing these co-dimer diene compounds.
Typical conjugated dienes used in the invention include isoprene and myrcene. The isoprene is reacted with a vinyl ester to prepare 4-methyl-5-hexen-1-al, which is a useful perfume material and can be used in a perfume composition. The invention relates also to this aspect.
Likewise, myrcene gives rise to 4-vinyl-8-methyl-7-nonenal which is also a useful perfume material. The invention relates therefore to 4-vinyl-8-methyl-7-nonenal, a method of production thereof and a perfume composition prepared therefrom. The 4-vinyl-8-methyl-7-nonenal has a strong, aliphatic aldehyde-like fragrance, emanating a citrus--as well as rose-like scent, and can be used as perfumes or in perfume compositions.
2. Description of Related Art
Generally, a small difference in chemical structures among compounds gives rise to a considerable difference in fragrances of the compounds and the other related properties, e.g. retentivity and volatility. The search for new perfumes involves therefore an important workload in such fields as synthesis of various compounds and tests of their fragrance. Among these compounds, aliphatic aldehydes are known as a useful source for perfume essence materials. From this viewpoint, many aldehydes have been produced and put to actual use (Motoichi INDO, "Synthetic Perfume", Chemistry and Product Information, 1996, published by Kagaku Kogyo Nippoh). For instance, melonal, citral and citronellal emanate a green melon-like, lemon-like and hawthorn-like fragrance, respectively, and give a specific scent to perfume compositions. They are therefore widely used as a blending essence for a perfume.
As for 4-methyl-5-hexen-1-al, a method of its production from citronellal is reported in J. Org. Chem., Vol. 42, pp. 3622, 1977. This method has the disadvantage of involving many steps and incurring high production costs. Moreover, there has been no description on the fragrant characteristics of 4-methyl-5-hexen-1-al, nor on its use as perfume compositions. Cis-3-hexenal, a compound similar to 4-methyl-5-hexen-1-al, is very expensive, and trans-2-hexenal, another similar compound, has a strongly irritant odor.
In order to form a carbon-carbon bond with butadiene or substituted butadienes efficiently, methods involving a Diels-Alder reaction (B. M. Trost et al., Angew. Chem. Int. Ed. Engl., Vol. 34, pp. 259 (1995)) and reactions with a triple bond (T. Mitsudo et al., J. Org. Chem., Vol. 50, pp. 565 (1985)) have been well-known.
All these methods, however, have the disadvantages that the conjugated double bond of butadienes or its counter part compound must be activated and the regioselectivity cannot be controlled.
Moreover, these methods are susceptible to forming ring products, which is a handicap for the synthesis of chain terpene.
Meanwhile, organometallic reagents have been widely used in reactions for synthesizing carbon-carbon bonds, so as to form desirable skeletons selectively (Japanese Patent Application Laid-Open (JP-A) No. H3-148228). However, these reactions not only involve use of a cumbersome organometal in a stoichiometric amount but also requires the so-called "elimination group", namely, a functional group which does not participate in the structure of the resultant product. This is a disadvantage from the industrial and environmental points of view, and the reactions become costlier. It is therefore desirable to develop a novel route for synthesizing a carbon-carbon bond. This novel route should involve the reaction which does not require any elimination group, and may proceed on a catalytic basis.